The field of the invention is that of optical cavities, in particular laser optical cavities.
Fabry-Pxc3xa9rot optical resonant cavities are defined longitudinally by first and second reflectors. All optical wavelengths for which the dimension of the cavity is equal to an integer number of half-wavelengths correspond to resonant modes of the cavity. Thus for a given dimension of the cavity there is an infinite number of wavelengths producing resonant modes. One prior art Fabry-Pxc3xa9rot cavity is made up of two mirrors. In another prior art cavity one of the reflectors is a Bragg reflector grating etched on a waveguide, for example a fibre. That kind of cavity has a plurality of resonant modes that correspond to wavelength values close to Bragg values for which there is a reflection peak of the reflector.
Both the above cavities have the common feature that the cavity resonates at discrete wavelength values.
A small number of non-resonant structures, such as light-emitting diodes and travelling wave amplifiers, generate continuous spectra. In structures of that kind the gain of the amplifier is subject to unwanted fluctuations, and if the unwanted fluctuations are eliminated, the gain becomes that of a single-pass travelling wave amplifier.
Resonant structures provide higher transmission coefficients than can be obtained with non-resonant structures, but are inherently highly sensitive to small variations of the wavelength (or optical frequency) of the transmitted light.
The invention therefore proposes a resonant cavity having a high transmission coefficient and a constant spectral response over a continuous range from a minimum frequency value to a maximum frequency value. This continuous range of frequencies corresponds to a continuous range of wavelengths between a maximum first value corresponding to the minimum frequency of the continuous range of frequencies and a minimum second value corresponding to the maximum frequency of the continuous range of frequencies. This is known in the art.
To the above ends, the invention provides a resonant optical cavity having a first part provided with a first waveguide oriented along a longitudinal axis on which an origin of distances is defined, the cavity being defined between first and second reflectors, the second of the reflectors being a variable pitch Bragg reflector grating on said first waveguide, said grating of the second reflector having one end near the first reflector and one end farther away from the first reflector, a parameter CS of variation of the Bragg wavelength defined as the derivative at a point on the reflector grating of the Bragg wavelength xcexB at that point with respect to the distance between that point and the origin having a given value, which cavity is characterized in that said value of the parameter CS and the position of said grating relative to the origin are such that the cavity formed between said first reflector and said second reflector resonates continuously from a first optical frequency to a second optical frequency higher than the first optical frequency.